The devices for heating a continuous flow fluid essentially consist of two components, a heating component consisting of one or more electrical resistors in thermal contact with the other component, essentially a conduit, or pipe, in which a liquid to be heated flows. These devices are used in automatic machines for coffee, tea, or more in general for hot drinks. In these machines the water must be brought to a certain temperature, for example approximately 90-100° C. for the preparation of coffee or 120-140° C. for the production of steam. The characteristic of these heat exchanger machines relates to the flow of the water that continuously flows along the pipe and that must therefore be brought to the right temperature in the short period of time passing between the entry of the water into the device and its exit from the device itself. This demands that the device must be able to provide a sufficient amount of heat to heat the water in this short period of time. These are therefore devices that must have a low thermal inertia, also to allow the passage from one function to another, such as, for example, from the water heating function to the steam generation function, in the shortest possible time. It is therefore necessary, in order to avoid having to resort to relatively long pipes, to provide systems in which the exchange of heat between the heating element and the water is particularly efficient. There are currently particularly efficient systems on the market called “flow through heater” (FTH) that typically consist of an extruded aluminium body with three through-holes. A pipe, for the most part made of steel, that is subsequently brazed, is inserted into the central hole, while the heating resistors are formed in the two side holes. FIG. 1 shows a device 100 of this type. The device represented in FIG. 1 consists, as mentioned, of an aluminium extrusion 1 wherein two heating resistors 2 and a steel pipe 3, where the water to be heated can flow, are formed.
Document DE8529085 describes a heating device having a body with an upper and lower face opposite to each other. Two respective continuous longitudinal grooves that primarily extend along the longitudinal axis of the heating elements are laterally present between the two faces, so as to leave a long portion thereof uncovered and not in contact with the body. The heater described in this document proposes to solve the problems linked to calcification and corrosion of the pipe for the fluid by coating the latter with a layer of plastic.
The problems that arise in the production of this type of device, in particular those of the flow through heater type, mainly relate to the high production waste in the brazing step and to functional repeatability. In addition, the brazing process used to join the steel pipe and the aluminium body together does not ensure 100% joining of the coupled surfaces of the two components.
In an embodiment thereof, document DE2555599 describes a heating device with a body and provided with a channel and a heating element. The heating element is provided with a plurality of peripheral projections that primarily extend along its longitudinal axis in order to anchor the heating element to the body. Moreover, in this case also, the body has an upper face and a lower face that are opposite to each other, between which a continuous longitudinal groove is laterally present at the heating element, which primarily extends along the longitudinal axis of the latter. Since this groove is present, one of the projections of the heating element is not covered by and is not in contact with the body. One disadvantage of the configurations of the above documents is indeed provided by the fact that a long portion of heating element is not in contact with the body, due to the long continuous longitudinal grooves that are laterally present. The exchange of heat between the heating element and the body, and thus with the fluid to be heated, is therefore substantially reduced. In addition, producing heating elements with longitudinal projections is relatively complex and expensive.
A further problem of the devices produced by extrusion relates to the difficulty of integrating the thermostat-holder platforms and the control sensor platforms that must be produced by the joining thereof to the aluminium body by welding and/or brazing, the problem of contact uniformity thus remaining. Another construction method used is the one that uses a low pressure aluminium or alloy die-casting process, which however has the disadvantage of being slow and therefore unprofitable for large production numbers. There is therefore a need to produce a new type of device for heating a continuous flow fluid that can overcome the described defects, is compact and has a high heat exchange efficiency, while also improving the speed of the production process.